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Got a couple P0440 DTC's the passed couple weeks. I had been hearing some rattling coming from my catalytic area under the car. Could a bad cat cause P0440's? Or should I do more investigating for the location of the rattle/reason for the code?

P0440 is an evaporative system leak code...the "check gas cap" code. Your rattling cat is a separate issue. This can be a bit tough for a DIYer to track down, due to the number of things that could set it. The vent valve, the purge valve, the gas cap, the pressure sensor, the gas tank, and all of the lines connecting it all. A shop can usually track it down easily with a smoke test.

To start, I'd suggest checking your filler tube under the gas cap. It can get quite rusty. Try cleaning that well, and then spray it with some rust reformer to hold the rust down, and then maybe a little top coat to protect it. See if that helps. As a test, you can try just cleaning it first, before putting on the coating. If this doesn't help, we can move on from there. You should get the code cleared after the cleaning, as it will take several cycles to reset the code if it does fix it.

I dealt with multiple P0440 as well as P0442 codes for a few months. Tried everything I could (polishing filler neck edge, lubing evap vent valve, replacing the fuel tank pressure sensor, and replacing the fuel cap), but nothing worked. Wound up taking it to a Chevy dealer, and having it smoke tested. Turned out to be the evap valve under the car. $250 total spent at the dealer, and ~ 75 bucks prior just guessing at *shoot*. Take it to the dealer if the CEL bothers you like it does me. Archon's advice is best. Asmoke test is your best bet.

Mark

Dang. Was just hoping fixing the cat would fix me up. I have a ScanGuage, so I've been clearing it myself. The first time I tightened my gas cap and reset the code... Then the code came back yesterday. I just cleared it and did nothing this time, as I figured it was something more.

Thanks for the advice guys. I'll try cleaning the cap up and looking for anything obvious in that area. I will take her to the dealer/shop if it comes back.

Had same code, took a guess after having it for about 3 months and just replaced my EVAP purge solenoid, fixed it.

01bonneSC wrote:Had same code, took a guess after having it for about 3 months and just replaced my EVAP purge solenoid, fixed it.

Same for me.

Well, mysteriously I haven't seen this code since cleaning around my gas cap. Hopefully that was the trick. I didn't see anything to nasty on there, but who knows. Although this intermittent problem could be hiding for now. Will keep an eye on things.

Mark Fahey wrote:

01bonneSC wrote:Had same code, took a guess after having it for about 3 months and just replaced my EVAP purge solenoid, fixed it.

Same for me.

Ditto for me